Which position you take in a search query via a search engine is not a random product. Rankings are subject to a constant SEO development.
Obviously SEO and SEA are in competition with each other. So many site operators are annoyed that they have worked hard to develop an SEO campaign together with an agency, but the best ranking is still achieved through paid SEA measures. In return, it is hardly lucrative to permanently place ads via Google AdWords and ignore the SEO.
On the other hand, understand the two variants SEO and SEA as two relevant measures of online marketing that you should promote in parallel. Here you use a fundamental, systematic difference:
SEO is basically free of charge, every site operator can reach top positions with the right measures without expensive expenditures. SEO has a long-term effect and can take several weeks or months to reach the desired positions.
SEA has an acute effect and gives you the opportunity to bid on top positions for specific search terms on a daily basis. This is worthwhile for new products or special promotions, for example. Through bidding, however, you pay money for search engine advertising.